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Abstract

This meta-analysis examined the mean sleep duration and patterns in Chinese older adult population. A literature search was systematically conducted covering major English (PubMed, Embase and PsycINFO) and Chinese (Chinese National Knowledge Infrastructure (CNKI), WanFang and SinoMed) databases. Data in studies with the mean and standard deviation of sleep duration and/or the proportion of short and long sleep durations in Chinese older adults were extracted and pooled using random-effects models. Subgroup analyses were conducted according to gender, region, area, survey time and sample size. A total of 36 studies with 150,616 subjects were included for analyses. The pooled mean sleep duration of 21 studies with available data was 6.82 hours/day (95% CI: 6.59-7.05 hours/day). The estimated proportions of sleep duration <5 hours/day, <6 hours/day, <7 hours/day were 18.8% (95% CI: 1.7%-35.9%), 26.7% (95% CI: 19.7%-33.7%) and 42.3% (95% CI: 34.8%-49.8%), respectively. The pooled proportions for long sleepers were 22.6% (95% CI: 13.9%-31.4%) (>8 hours/day) and 17.6% (95% CI: 12.4%-22.9%) (>9 hours/day). Given the adverse effects of unhealthy sleep patterns, health professionals should pay more attention to sleep patterns in this population in China.

Keywords: Sleep duration, old adult, meta-analysis, China.

Introduction

Sleep pattern is closely associated with health and well-being. Emergent evidence indicates that both insufficient and excessive sleep durations are linked with poor physical and mental health [1-6]. In addition, a U-shaped relationship between sleep duration and mortality was found in many studies [7, 8]. Understanding the distribution of sleep duration and sleep patterns in a population is essential for health professionals to examine the sleep-related health problems and implement effective measures to improve unhealthy sleep habits.

Population aging has been a growing health challenge worldwide, especially in developing countries, such as China [9, 10]. The Chinese Ministry of Civil Affairs reported that the number of elderly persons aged 60 years and above have reached 222 million in China, accounting for 16.1% of the whole population at the end of 2015 [11]. Sleep problems including short and long sleep durations have been common in older adult population globally [1-6, 12]. In China, sleep patterns have been found to vary greatly across different studies [13-15]. One major reason is lack of gold standard criterion of short and long sleep duration. The recent recommendation made by the National Sleep Foundation suggested that different sleep durations are appropriate for different age groups [16]. Older people aged 65 years and above were recommended to sleep 7-8 hours per day; less than 5 or more than 9 hours per day are not recommended [16].

To the best of our knowledge, there have been no meta-analysis or systemic review of the sleep duration and patterns among older adults in China. The objective of this study was to summarize the data from observational studies and then estimate the mean sleep duration and proportion of short and long sleepers in Chinese older adult population.

Methods

Search strategy

This meta-analysis was performed based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. Two reviewers (LL and RWW) identified studies independently from PubMed, Embase, PsycINFO, Chinese National Knowledge Infrastructure(CNKI), WanFang, SinoMed from inception until September 10, 2016, using the search terms as follows: (sleep time OR sleep duration OR sleep habit OR sleep pattern OR insomnia OR sleep problem OR sleep disturbance OR sleep disorder OR sleep quality OR sleep symptom) AND (epidemiology OR cross-sectional study OR prevalence OR rate) AND (older adults OR elderly OR aged OR aging) AND (China OR Chinese). Additional studies were searched manually from the references of the selected publications.

Study selection

Studies that met the following criteria were included: a) cross-sectional or cohort studies conducted in China; b) sleep duration expressed as mean and standard deviation (SD) or as the proportion of short (<5 hours/day, <6 hours/day, or <7 hours/day) and long (>8 hours/day or >9 hours/day) sleep duration in adults aged ≥60 years according to the recommendation by the Chinese Ministry of Health; c) sample size ≥100; d) availability in full text in Chinese or English. For cohort studies, only the baseline data were extracted for analyses.

Studies on special populations (e.g., army, retired people, empty nesters, people with major medical conditions) or specific settings (e.g., hospitals or nursing homes) and those using convenience sampling or without details on sampling process were excluded.

Two reviewers (LL and RWW) screened titles and abstracts of the initial search results independently. If there were more than one article based on the same study, only the one with the largest sample size and complete information was included for analysis.

Data extraction and quality assessment

Two reviewers (LL and RWW) conducted the data extraction independently. Disagreements emerged in the procedures were resolved by a discussion with a third reviewer (WSB). The following information was extracted and tabulated: study setting, sampling method, sample size, characteristics of the participants, and sleep duration with quantitative data. If there was more than one arm using different cut-offs of sleep duration in one study, then these arms were analyzed separately. The quality of included studies was assessed using the 22-item Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) [17]. In this meta-analysis, studies with a score of >11 were rated as “good quality” [18].

Statistical analysis

The pooled mean of sleep duration, proportion of short and long sleep durations, and their 95% confidence intervals (CI) were calculated using random-effects models. The bedtime, sleep latency, time to go to bed and to get up were also pooled. Heterogeneity between studies was measured by I2 statistic; I2>50% was considered as high heterogeneity [19]. Subgroup analyses were performed to explore possible sources of heterogeneity according to age groups (60~/70~/≥80 years old; for sleep duration only), gender, area (rural/urban), region (east, central and west parts of China according to the Chinese economic zone division), sample size and survey time (dichotomized using median splitting method). If there were more than 10 studies, meta-regression models were used to detect heterogeneity for continuous variables [20]. Funnel plots, Begg's test [21] and Egger's regression model [22] were used to evaluate publication bias. Sensitivity analysis was carried out by removing each study individually to evaluate the consistency of the results. Comprehensive Meta-Analysis software version 2 (Biostat Inc., Englewood, New Jersey, USA) was used to perform the subgroup analyses and STATA version 12.0 (Stata Corporation, College Station, Texas, USA) was used to conduct other analyses. Significance level was set at 0.05 (two-tailed).

Results

Studies selection results and basic characteristics

A total of 6,598 potential papers were identified, of which 36 papers published in English (n=10) and Chinese (n=26) with 150,616 subjects met the selection criteria and were included for analyses (Figure 1). A total of 21 studies reported mean and SD of sleep duration, 22 studies reported the proportion of short sleepers (15 studies reported the data of sleeping <6 hours/day and 11 studies reported the data of sleep <7 hours/day) and 17 studies reported the proportion of long sleepers (10 studies reported the data of sleeping >8 hours/day and 9 studies reported the data of sleep >9 hours/day). One study provided data of Han and Korean Chinese separately, therefore we extracted and analyzed the data as two arms [23]. Comprehensive characteristics of the eligible studies are shown in Table 1.

Quality assessment and publication bias

The mean STROBE score of the studies was 18, ranging from 14 to 21. All studies were classified as good quality. Supplemental Figure 1 shows the funnel plot of the 21 studies with mean and SD of sleep duration, the Begg's (Z=-1.15, P=0.264) and Egger's tests (t=-0.44, 95%CI: -19.1-12.5, P=0.667) did not reveal any publication bias. Similarly, no publication bias was found in other meta-analyses (Table 2).

Sleep duration of Chinese elderly

The meta-analysis revealed that the mean sleep duration was 6.82 hours/day (95% CI: 6.59-7.05 hours/day) (Figure 2). The proportion of short and long sleepers are presented in Table 2. The proportion of short sleepers was 18.8% (95% CI: 1.7%-35.9%), 26.7% (95% CI: 19.7%-33.7%) and 42.3% (95% CI: 34.8%-49.8%), when defined as less than 5 hours/day, 6 hours/day and 7 hours/day, respectively. In contrast, the proportion of long sleepers was 22.6% (95% CI: 13.9%-31.4%) and 17.6% (95% CI: 12.4%-22.9%), when defined as more than 8 hours/day and 9 hours/day, respectively.

Figure 1

Flowchart of the selection of studies

(Click on the image to enlarge.)

Table 1

Characteristics of included studies

No.

Author(Publication year, language)

Samplingmethod

Survey time(year)

Samplesize

Age (years)

Urban/Rural

Female (%)

City/Province

Area

Sleep information

STROBE score

Mean

SD

1

Ding X.J. (1997, C)

S, C, R

1992

2779

NR

NR

Mixed

NR

Beijing

East

M, <6, >9

14

2

Chiu H.F.K. et al. (1999, E)

S, R

1995

1034

NR

NR

Urban

51.26

Hong Kong

East

M, SD

21

3

Liu L.Q. et al. (2001, C)

S, C, R

1997

1805

70.62

5.27

Urban

52.47

Jinan,Wendeng,Liaocheng, Zaozhuang,Binzhou/Shandong

East

M, SD, TB, SL, TG

20

4

Lin D.Y. et al. (Han) (2005, C)

R

2004

469

67.7

6.0

Urban

54.37

Yanji/Jilin

Middle

M, SD, TB, TG, BT

16

5

Lin D.Y. et al. (Korean) (2005, C)

R

2004

494

68.5

6.2

Urban

67.00

Yanji/Jilin

Middle

M, SD, TB, TG, BT

16

6

Zhang Q.H. et al. (2006, C)

M, R

2004

25061

71.2

9.5

Urban

NR

Beijing

East

M, SD, <6,>8, TB, SL, TG, BT

15

7

Lan T.Y. et al. (2007, E)

M, PPS

1993

3079

71.28

5.58

NR

43.23

Taiwan

East

<7,>8,>9

19

8

Liu Y. (2007, C)

C, R

2005

2304

74.5,

7.7

Urban

57.94

Shanghai

East

M, SD, TB, SL

20

9

Yao K.W. et al. (2008, E)

M, R

NR

187

72.13

4.93

Urban

48.66

Taipei

East

M, SD, SL, BT

20

10

Liu A.L. (2008, C)

R, C

NR

5390

NR

NR

NR

51.54

Zhengzhou,Kaifeng/Henan

Middle

<6, >9

18

11

Xiang Y.T. et al. (2009, E)

S, M, PPS

NR

1141

NR

NR

NR

NR

Beijing

East

<7,>8

20

12

Liu H.L. et al. (2009, C)

S, C, R, PPS

2006

664

NR

NR

Urban

53.92

Shijiazhuang/Hebei

East

M, SD, TB, SL, TG

18

13

Li J. (2009, C)

R

2006

1006

NR

NR

Mixed

NR

Tianjin

East

M, SD

17

14

Li H. et al. (2009, C)

C, R

2007

4237

NR

NR

NR

56.86

Fuzhou/Fujian

East

<6, >9

15

15

Gu D. et al. (2010, E)

R

2005

15638

NR

NR

Mixed

57.23

22 provinces

M, SD, <7,>9

17

16

Li J. (2010, C)

S, C, R

2009

1680

68.44

7.1

Rural

49.94

Anhui

Middle

M, SD, TB, TG

20

17

Xie Z. et al. (2010, C)

S, C, R

2009

1040

70.1

7.4

Rural

48.08

Hengyang/Hunan

Middle

M, SD, <5, <6, <7,>8,>9, TB, TG

19

18

Wang W. et al. (2011, C)

R, C

NR

145

63.91

2.94

Urban

55.17

Beijing

East

<6, >8

17

19

He M.H. (2011, C)

R, C

2010-2011

1200

65.6

6.7

Rural

36.25

Hong'an/Hubei

Middle

M, SD

15

20

Chen Z.Y. (2011, C)

S, R

NR

312

69.1

NR

Rural

58.65

Western Hunan

Middle

<6, >9

17

21

Wu C.Y. et al. (2012, E)

R

2001

100

74.7

5.3

Urban

55.00

Taipei

East

<5, <7

20

22

Wang Q. et al. (2012, C)

R, S, C

2011

404

71.18

6.61

Urban

63.12

Xi'an/Shannxi

West

M, SD

19

23

Li S.X. et al. (2012, C)

R, C

2008-2009

753

67.9

7.05

Urban

51.13

Tangshan/Hebei

East

<5, <6, <7

18

24

Luo J. (2013, E)

C

NR

1086

72.2

8.3

Urban

57.27

Shanghai

East

M, SD, <6, <7,>8, SL, BT

20

25

Zhu Y.J. et al. (2013, C)

M, S, R, C

2012

4115

65.89

4.95

Mixed

51.01

Jilin

Middle

<6

18

26

Yue J. et al. (2013, C)

S

2011-2012

758

72.25

8.25

NR

43.93

Xi'an/Shannxi

West

<6, >8

18

27

Liu J.F. et al. (2014, C)

M, R, S

2012-2013

5470

74.56

6.73

Urban

47.04

Changsha/Hunan

Middle

M, SD

20

28

Zhang Y. et al. (2014, C)

C

2012

1500

70.24

8.44

Urban

49.33

Tangshan/Hebei

East

<5, <6, <7

19

29

Zhao J.X. et al. (2014, C)

R

2010

358

NR

NR

Urban

45.81

Guangzhou/Guangdong

East

>8

18

30

Yu S. et al. (2015, E)

M, S, R, C

2012-2013

1717

71.18

4.97

Rural

49.45

Liaoning

Middle

M, SD

20

31

Wang X.J. et al. (2015, C)

S, R

NR

526

70.24

NR

Rural

52.28

Shan county, Cao county/Shandong

East

<6

17

32

Wang K.Y. et al. (2015, C)

S, C, R

2013

4002

73.34

6.01

Rural

51.42

Yichang/Hubei

Middle

M, SD, <7,>9

20

33

Liu H. et al. (2016, E)

M, S, PPS

2011-2012

5616

NR

NR

NR

47.19

28 provinces

M, SD, <6, <7,>8

20

34

Zhi T.F. et al. (2016, E)

S, R

2014

1756

75.3

3.9

Rural

53.30

Rugao/Jiangsu

East

<6, >8

19

35

Lv Q.J. et al. (2016, C)

C, R

NR

820

70.7

5.9

Urban

52.32

Pingdingshan/Henan

Middle

<5,>9

21

36

Qi S.G. et al. (2016, C)

M, S, C, R

2013

51774

NR

NR

Mixed

54.81

31provinces, Xinjiang Production and Construction Corps

M, SD, <7

19

37

Zhong X.X. et al. (2016, C)

S, C, R

2014

196

70.2

7.3

Rural

52.55

Ma'anshan/Anhui

Middle

M, SD

17

NR=Not Reported; SD= Standard deviation; C; Chinese, E: English.

Sleep Information: M=mean of Sleep duration; SD=standard deviation; <5 refers to the percentage of participants with a sleep duration<5 hours/day, <6 refers to that <6 hours/day, <7 refers to that <7 hours/day,

>8 refers to that >8 hours/day and >9 refers to that >9 hours/day; TB=time to go to bed, SL=sleep latency, TG=time to get up, BT=bed time.

The results of subgroup analyses using mean sleep duration, the proportion of long (>9 hours/day) and short sleep (<6 hours/day) are shown in Table 3. The results using other cut-offs for sleep duration are shown in Table S2. The proportion of short sleepers (<6 hours/day) was 38.3% (95% CI: 20.7%-59.6%) in rural areas, while it was 17.0% (95% CI: 8.6%-30.8%) in urban areas, but the difference did not reach a significance level. Meta-regression analyses revealed that sample size and survey time did not have significant impact on the results (P>0.05).

The time to go to bed for older adults in the east area was later than in the middle area (09:23 pm, 95% CI: 09:06 pm - 09:41 pm vs. 08:43 pm, 95% CI: 08:27 pm - 09:00 pm), but the former group had longer bedtime than the latter group (8.10 hours, 95% CI: 7.87 hours - 8.33 hours vs. 7.41 hours, 95% CI: 7.13 hours - 7.70 hours). Subgroup analyses of sleep habits are shown in the Table S3.

Sensitivity analyses

After removing each study sequentially, the results from remained studies were still consistent with the primary results.

Table 3

Subgroup analyses of sleep duration

A. Subgroup analyses of night sleep duration

Subgroups

Categories(Number of studies)

Mean

SE

95%CI

Sample size

I2(%)

P

Q (P)

Age groups(years)

60~ (4)

6.68

0.41

5.88

7.48

2748

99.4

<0.001

0.33(0.85)

70~ (4)

6.53

0.41

5.73

7.33

2957

99.5

<0.001

≥80 (4)

6.86

0.41

6.05

7.67

1504

98.9

<0.001

Gender

Female (11)

6.52

0.18

6.12

6.86

6666

99.0

<0.001

1.33(0.25)

Male (11)

6.81

0.18

6.46

7.15

5823

98.3

<0.001

Region

Rural (6)

6.63

0.22

6.19

7.07

9835

99.8

<0.001

0.59(0.44)

Urban (11)

6.84

0.17

6.52

7.17

38978

99.4

<0.001

Sample size

≤1500 (11)

6.66

0.17

6.33

6.99

7780

99.5

<0.001

1.90(0.17)

>1500 (10)

7.00

0.17

6.65

7.34

115067

99.9

<0.001

Area

East (11)

6.94

0.20

6.55

7.33

50502

99.8

<0.001

1.31(0.52)

Middle (8)

6.77

0.22

6.33

7.21

14551

99.7

<0.001

West (1)

6.21

0.08

6.06

6.36

404

-

-

Survey time

1999-2010 (10)

6.75

0.19

6.38

7.12

49515

99.8

<0.001

0.16(0.69)

2011-2016 (9)

6.86

0.20

6.47

7.26

72059

99.8

<0.001

Language of publications

Chinese (15)

6.82

0.15

6.52

7.10

97569

99.8

<0.001

0.04(0.85)

English (6)

6.86

0.24

6.40

7.32

25278

99.7

<0.001

B. Subgroup analyses of the rate of short sleep duration (<6 hours/day)

Subgroups

Categories(Number of studies)

Proportion (%)

95%CI (%)

Events

Sample size

I2(%)

P

Q (P)

Region

Rural (4)

38.3

20.7

59.6

1792

3634

99.2

<0.001

3.48(0.06)

Urban (5)

17.0

8.6

30.8

9176

28545

99.2

<0.001

Sample size

≤1700 (8)

21.0

14.8

28.9

1517

6120

99.4

<0.001

1.36(0.24)

>1700 (8)

27.7

19.7

37.5

15225

48954

99.6

<0.001

Area

East (9)

19.0

12.4

27.9

11335

37843

99.5

<0.001

3.89(0.14)

Middle (4)

35.9

20.9

54.3

3330

10857

99.7

<0.001

West (2)

30.0

12.9

11.9

835

2416

98.8

<0.001

Survey time

1997-2012 (5)

29.8

18.8

43.9

10762

33870

99.7

<0.001

0.16(0.69)

2013-2016 (5)

26.3

16.2

39.6

4557

13745

99.4

<0.001

Language of publications

Chinese (12)

24.9

17.0

32.8

13740

46616

99.5

<0.001

1.30(0.25)

English (3)

33.8

15.3

52.3

3002

8458

99.5

<0.001

C. Subgroup analyses of the rate of long sleep duration (>9 hours/day)

Subgroups

Categories(Number of studies)

Proportion (%)

95%CI (%)

Events

Sample size

I2(%)

P

Q (P)

Region

Rural (4)

18.7

13.5

25.2

3745

14013

98.6

<0.001

0.94(0.33)

Urban (2)

24.1

15.7

35.2

2059

7799

91.7

<0.001

Sample size

≤3100 (5)

17.9

11.7

26.4

1805

8030

98.8

<0.001

0.51(0.48)

>3100 (4)

14.3

8.8

22.4

4455

29267

99.5

<0.001

Area

East (4)

23.3

14.2

35.8

4013

16182

99.3

<0.001

1.64(0.44)

Middle (6)

15.8

10.2

23.6

3022

16224

99.5

<0.001

West (1)

23.3

21.7

25.0

582

2497

-

-

Survey time

1997-2006 (3)

21.0

12.5

33.0

3917

21496

99.6

<0.001

0.66(0.42)

2007-2013 (3)

15.6

9.0

25.6

1798

9279

98.9

<0.001

Language of publications

Chinese (8)

15.7

11.0

20.4

5244

34218

99.0

<0.001

4.36(0.04)

English (1)

33.0

31.3

34.7

1016

3079

-

-

Discussion

In this meta-analysis, the pooled data of 21 studies showed that the mean sleep duration in Chinese older adults was 6.82 hours/day. In this group, 26.7% reported sleeping less than 6 hours and 17.6% sleeping more than 9 hours per day. On average, they went to bed at 09:03 pm and got up at 05:24 am. Their mean time spent in bed was 7.82 hours during which they needed 30.66 minutes to fall asleep. In terms of subgroup analysis, a greater proportion of older adults in rural areas had short sleep duration (<6 hours/day) than their urban counterparts.

The mean sleep duration in this meta-analysis (6.82 hours/day) is shorter than the duration (7.5 hours/day) from another large survey of 15,638 older Chinese adults in 22 provinces [13], but is similar to that found in Europe (6.95 hours/day) [24]. A multi-ethnic study on sleep duration showed that the proportions of short sleepers in white, black, Hispanic and Chinese people were 19.3%, 43.4%, 31.5% and 37.1%, respectively [25]. Apart from the use of different definitions of short sleep, other factors, such as living rhythm, lifestyle, sleeping environment, chronic medical conditions, psychiatric disorders and outdoor activities, are significantly associated with sleep duration in older adults [24, 26].

China has been experiencing rapid urbanization and economic growth in the past decades, which may have a negative impact on the health of older adults [27]. For example, increased consumption of stimulant drinks, such as tea, coffee and energy drinks, increasing nightlife and widespread use of electronic devices often interfere with 'circadian rhythm' including sleep pattern. However, the survey year of the included studies did not show a significant moderating effect on sleep duration in subgroup analysis.

There is compelling evidence that short sleep duration could increase the risk of obesity, coronary heart disease, all-cause mortality, and was an important risk of non-successful aging [1, 5, 28, 29]. In contrast, long sleep duration was positively associated with cardiovascular diseases, stroke and mortality [1, 2, 4, 28]. Moreover, cognition and memory impairment were common in both short and long sleepers [3, 6, 30-32].

Previous studies found that low economic status is associated with greater sleep disturbance and short or long sleep duration [33, 34]. Considering that economic status is higher in the eastern region and urban areas than in the central region and rural areas in China, subgroup analyses were conducted between different areas defined by the Chinese economic zone. We found the proportion of short sleepers (<6 hours/day) in rural area (38.3%) was higher than in urban area (17.0%); the proportion in central region (35.9%) was higher than in the eastern region of China (19.0%), which support the association between economic status and sleep pattern. In addition, we found that Chinese older adults usually go to sleep almost an hour earlier than their counterparts in the USA, while the sleep latency of the Chinese old people were similar to those in the USA and Europe [24, 35].

The results should be interpreted with caution due to several limitations. First, inconsistent criteria were used in assessing the sleep duration across studies [36]. Second, sleep data were self-reported which may lead to recall bias. Third, heterogeneity remained in the subgroup analyses, since heterogeneity cannot be avoided in large meta-analysis of epidemiological surveys [37-39].

In conclusion, short sleep duration is common in Chinese older adults. Given its adverse effects, effective measures should be implemented to improve the sleep patterns in this population.

Supplementary Material

Acknowledgements

The study was supported by the University of Macau (SRG2014-00019-FHS; MYRG2015-00230-FHS; MYRG2016-00005-FHS). The University of Macau had no role in the study design, generating or interpreting the results and publication of the study.

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